The first skill that a coach learns is how to identify problems. Go poolside with a beginner coach and they will talk your ear off about what the athletes need to fix. A healthy coaching instinct says "I think I can help" and sets off to "correct" people's problems.
But fixing problems is only scratching the surface of what coaching is all about. Everybody is a critic, and it's easy to sit and criticize others. It takes only slightly more effort to rage at their inadequacies and make them fear your wrath if their "mistakes" continue.
It's hard to look at people, figure out what they are doing right, what has made them as successful as they are to this point, and nurture it. Many in the coaching profession rely on a critical bent to establish their "authority" over their athletes. Praising people for what they are doing right looks "soft" to them. Nothing could be farther from the truth.
The best in the sport all have significant weaknesses. No amount of correction and shoring up will fix that. Just look at the recently finished career of Michael Phelps, who any sane person agrees is the top performer the sport has ever seen. He had plenty of problems that went unfixed through fifteen years of international stardom.
If your coach is only focused on your problems, you will be chasing an ever moving target, never knowing if you're actually making progress. Worse yet, you will feel like you have a never-ending list of problems, instead of real strengths that can help you be successful.
What's interesting is that what comes so naturally in an educational setting gets thrown out the window in sports. Think about a math class where you were never aware of what you already know.
Inexperienced swimmers and coaches often set off to endlessly tinker, to keep correcting without knowing what was right in the first place. Criticism is fine- but it should only be a small part of the feedback an athlete gets.